Soil moisture and salt ionic composition effects on species distribution and diversity in semiarid inland saline habitats, northwestern China

Salinization is one of the main types causing land desertification in arid and semi-arid regions. Little is known about the impacts of salinization on the distribution and diversity of plant species, especially in semiarid inland saline habitats. We established a total of 40 sampling plots to determine plant community (floristic composition, species abundance, cover, frequency, and aboveground biomass) and soil characteristics (moisture, pH, electrical conductivity (EC), and the contents of Na+, K+, Ca2+, Mg2+, Cl−, SO42− and HCO3−). The TWINSPAN method was used to distinguish plant communities, by which three plant communities (I, II, III) were identified, namely Artemisia scoparia + Agropyron cristatum + Sophora alopecuroides (I), Kalidium gracile + Atriplex centralasiatica (II), and Salicornia europaea + Suaeda salsa (III). From I to III, the indices reflecting species diversity all decreased except for Pielou’s index of evenness, while the aboveground biomass and cover increased; the characteristic indices of soil moisture, EC, the contents of Na+, K+, Ca2+, Mg2+, Cl−, SO42− and total dissolved salts (TDS) significantly increased, while the Ca2+/Na+, K+/Na+ ratios and HCO3− content significantly decreased. Canonical correspondence analysis (CCA) showed that the most important environmental factors influencing species distribution were: soil moisture, SO42−, K+/Na+ and pH. Stepwise multiple-regression analysis indicated that species richness was correlated mainly with TDS and moisture. These results also suggested that vegetation can be used as a proxy indicating soil salt conditions, and their relationships can further provide important information for the improvement of salt-affected soil’s management and salt-tolerant species utilization in environmental restoration.